Physicians employ tissue ablation to treat various medical conditions, including cardiac rhythm disfunction and benign prostatic hypertrophy. Tissue ablation is the process of directing energy to the target tissue site to form a lesion. The energy delivered may be in the form of radio frequency, microwave, ultrasound, light energy, and cryogenics, among others. In the case of the treatment of cardiac disfunction, lesions of different shape and size have been used to treat atrial fibrillation and ventricular tachycardia, among others.
Percutaneous transluminal ablation (PTA) catheters are frequently used for cardiac tissue ablation. The PTA catheters are long, slender, and flexible such that they can be inserted through a small incision through the skin into a blood vessel, such as an artery or vein, and advanced to the treatment site. Once positioned, the PTA catheter is used to selectively ablate or "burn" selected tissue which results in a change in the physiology of the treatment site. Such treatments may be used to block electrical conduction to correct abnormal cardiac rhythm that interferes with proper organ function.
PTA catheters use any of a number of methods to deliver ablative energy to the tissue. Some of these methods utilize radio frequency and microwave. The energy delivery component of the PTA catheter, sometimes referred to as an ablating element or electrode, is located either at the distal tip or along a portion of the distal end of the PTA catheter. When the PTA catheter is advanced through the blood vessel to the treatment site, either the tip or the side of the PTA catheter, depending on electrode type, is pressed against the tissue to be ablated.
Creation of linear lesions in the right and left atrium results in a progressive increase in the organization of atrial activity until sinus rhythm is restored. M. Haissaguerre, et al., reported successful ablation of atrial fibrillation in a patient with paroxysmal atrial fibrillation by the creation of three linear lesions in the right atrium, two longitudinal and one transverse, that connected the two longitudinal lesions using a specially designed catheter (Haissaguerre M, Gencel L, Fischer B, Metayer P L, Poquet F, Marcus F I, Clementy J., Successful Catheter Ablation of Atrial Fibrillation, J Cardiovasc Electrophysiol 1994;5:1045-1052).
Successful ablation therapy is defined as a return to normal sinus rhythm. To achieve this, lesions need to be continuous, transmural, and connected with other lesions or anatomical structures that cause blockage of atrial conduction. The seven recommended lesions are as follows: 1) right atrial isthmus ablation: linear lesion applied to the right atrium between the tricuspid annulus and the eustachian ridge, 2) right atrial inter-caval ablation: linear lesion applied along the posterior wall of the right atrium, between the superior vena cava and the inferior vena cava, 3) right pulmonary vein ablation (RPV): linear lesion applied to the left atrium, beginning below Bachmann's bundle, across the right superior pulmonary vein (RSPV) to the right inferior pulmonary vein (RIPV) and adjoining the mitral annulus, 4) left pulmonary vein ablation (LPV): linear lesion applied to the left atrium, beginning below Bachmann's bundle, across the left superior pulmonary vein (LSPV) to the left inferior pulmonary vein (LIPV) and reaching the mitral annulus, 5) superior pulmonary vein ablation (SPV): linear lesion applied to the left atrium, across the right superior pulmonary vein to the left superior pulmonary vein, 6) left atrial roof ablation (ROOF): linear lesion applied from the trigone, across the roof of the left atrium, to the left superior pulmonary vein, and 7) left atrial septal ablation (SEP): linear lesion applied to the foramen ovale to the right superior pulmonary vein. During creation of the right atrial inter-caval line, pacing is performed from each pair of electrodes at high output to assure the absence of diaphragmatic stimulation.
PTA catheters are designed for and have been used successfully for transluminal use; that is, via minimally invasive surgery. There is a need to have the capability to apply ablation therapy non-transluminally, such as during open heart surgery. For example, some patients having surgery for the treatment of atrio-ventricular valve disease would benefit from ablation therapy in order to correct cardiac arrhythmias of the atria or ventricle. Up to 40% of patients requiring mitral valve replacement have concurrent atrial fibrillation (fast atrial arrhythmia) which can be treated by creation of long linear ablation lines in the atria. During the open heart procedure, the physician is presented with a direct view of the target tissue to which ablation therapy may be applied, negating the need to approach the site transluminally. PTA catheters are inadequate for use in the open heart procedure, as they lack the structural support required to direct and press the electrodes against the target site. Also, due to their need to traverse narrow, tortuous vasculature, there is a definite limitation as to electrode size, shape and configuration available from PTA catheters.